COP: “We recovered the murder weapon, it had your fingerprints on the trigger!”
CRIM: “Uh, you got me. I did it! And you’ll never take me alive, copper!”
SFX Contagious Firing.
CRIM falls dead. COP and PARTNER high-five.
And that’s just the way it happens, right? Er, not right. While TV fingerprints relentlessly follow the laws of screenwriting, real fingerprints respond to the laws of physics. Even if the criminal took no measures to hide his fingerprints, they are a lot rarer and harder to recover than most people know.
This is a separate question from whether fingerprint IDs are accurate. A small study sponsoed by the National Academy of Sciences found a 7.5% false negative rate, and a 0.1% false positive rate, in testing of actual print examiners. If the study is representative, 1 in 1000 print identifications is wrong. Most defense attorneys know better than to challenge that: jurors, too, watch CSI: Laboratory Magick and other TV shows.
And this is a separate question from whether the examiner is working honestly, or falsifying evidence, as a string of recent scandals shows.
Ed Hueske of the University of North Texas, in Firearms and Fingerprints, one of a 7-volume set of popular books on forensic science published by Facts on File, generally cheerleads for the modern beau ideal of the forensic technician as a putatively objective scientist who just happens to be a full member of the police-prosecution team. But even he notes:
It is widely accepted as unlikely, for example, that identifiable fingerprints will be found on firearms. Identifiable fingerprints will be found probably less than 10 percent of the time. 1
In the author’s experience identifiable fingerprints are found on guns, knives, clubs, and the like in less than 10 percent of the cases. This is due to a number of factors including the surface characteristics of the weapon and the way in which the weapon was handled. On the other hand it is not uncom- mon to find some evidence of the handling of weapons in the form of partial fingerprint impressions, even though these partial impressions usually fall short of being identifiable to a specific individual.
Some types of evidence simply do not tend to retain any evidence of fingerprints, even when touched. Textured surfaces such as vehicle steering wheels, plastic milk jugs, and suitcase handles seldom show any sign of even having been touched. Other problems can include intense heat, humidity, and/or precipitation, which effectively destroy the fin- gerprints. Thus the probability of finding identifiable fingerprints on fired cartridge cases left at the crime scene, for example, is remote; the combination of the curved surfaces and the heat produced upon discharge tends to vaporize the fingerprints.2
Malvo was implicated as a shooter through a fingerprint found on the weapon and a fingerprint found on a cartridge case near one of the scenes. Finding identifiable fingerprints on weapons and fired cartridge cases is pretty uncommon, making this a stroke of good luck for investigators.3
He goes on to caution:
When a suspect’s fingerprints are not found on a murder weapon, however, defense attorneys often present this fact as an indication of their client’s innocence.
Likewise, the forensic scientist must take care not to inflate the significance of the physical evidence that is present. For instance, investigation might turn up a partial fingerprint that cannot be positively identified as belonging to a particular individual. To describe such a print as “consistent with” having been made by a suspect without explaining the other possibilities (namely that numerous other persons could be responsible) would be misleading.4
Many of the practitioners of this art seem untroubled by the possibility of their testimony being misleading. Some of them will even testify that not finding fingerprints on a firearm (where we have just learned that they are unlikely to be found is evidence in itself, of “conspicuous absence.”
…in the investigation of shooting deaths, the question of suicide versus homicide often comes up. If iden- tifiable fingerprints actually happen to be present on a weapon and they do not belong to the victim, homicide might be indicated. On the other hand, if fingerprints are conspicuous by their absence, further investigation is warranted.5
And Huelske goes on to reiterate that fingerprints are seldom found on guns or other weapons, and what this means:
While juries are often persuaded to believe that fingerprints would have to be left on a gun or a knife if a person handled it, nothing could be further from the truth. Consider, for example, weapon design. The surfaces that are typically handled on weapons are by design textured so as not to be slippery. While it is certainly possible to leave a finger- print on a weapon, in many instances it almost requires an overt effort to do so. Likewise, if a person had just washed and dried his or her hands prior to handling a weapon, it would be improbable that any fin- gerprints would be deposited. While it is still important always to test a weapon for fingerprints and not simply assume none will be found, it is more likely than not that the weapon will bear no fingerprints.
There are all sorts of explanations for why evidence might not be found, such as the following:
• It was never there to begin with.
• It was present but was removed prior to testing.
• The testing was improperly carried out.
The real point, again, is that negative evidence of any sort has no real significance beyond the fact that it was not found.6
Fingerprint evidence is very important to crime fighting. It works because most criminals start with small crimes and work their way up, so by the time they commit a crime that’s worth collecting fingerprint evidence at — as many outraged home owners and business managers have found, this usually isn’t a burglary or other property crime, but because it’s one of the forms of self-incrimination not protected by the Constitution. (Only speech-related testimonial self-incrimination falls under the 5th Amendment exclusion; physical self-incrimination, such as by fingerprint, DNA, handwriting, etc. is excepted).7
But fingerprint evidence is not magic, and it’s not readily recovered from guns; and that recovery is preventable with simple precautions, which are unfortunately taught from criminal to criminal in prison, and easily enough deduced by a reasonably intelligent person who investigates how fingerprint evidence is collected, developed and evaluated.
In fact, they’re more likely (if they try) to recover fingerprints from inside disposable gloves used by a criminal, than from a pistol handled directly by that criminal with bare hands. Food for thought, and that much more evidence that TV crime and investigation shows are made by people unfamiliar with crime or investigation.
- Hueske, p. xvii
- Hueske, p. 2.
- Hueske, p. 12.
- Hueske, p. xvii-xviii.
- Hueske, p. 15.
- Del Carmen, pp. 370-371, 474-475, G-7.
Del Carmen, Rolando V. Criinal Procedure: Law and Practice, 7/e. Belmont, CA, 2007: Thomson Higher Education. (This is a very dry criminal law textbook).
Hueske, Edward. Firearms and Fingerprints. New York, 2009: Facts on File. (Note that this isn’t a book on finding fingerprints on firearms, exclusively. It covers both fingerprint examination, including prints on firearms and other weapons, and firearms examination, a completely different discipline.